1. Field of the Invention
The present invention relates to a radio-frequency device, wireless communication device and method, and more particularly, to a radio-frequency device, wireless communication device and method capable of enhancing antenna isolation and maintaining throughput.
2. Description of the Prior Art
An electronic product with a wireless communication function, e.g. a laptop, a personal digital assistant, etc., utilizes an antenna to emit or receive radio waves, to transmit or exchange radio signals, so as to access a wireless network. Therefore, to facilitate a user's access to the wireless communication network, an ideal antenna should maximize its bandwidth within a permitted range, while minimizing physical dimensions to accommodate the trend for smaller-sized electronic products. Additionally, with the advance of wireless communication technology, electronic products may be configured with an increasing number of antennas. For example, a long-term evolution (LTE) wireless communication system and a wireless local area network standard IEEE 802.11n both support multi-input multi-output (MIMO) technology, i.e. an electronic product is capable of simultaneously receiving and transmitting wireless signals via multiple (or multiple sets of) antennas, to vastly increase system throughput and transmission distance without increasing system bandwidth or total transmit power expenditure, thereby effectively enhancing spectral efficiency and transmission rate for the wireless communication system, as well as improving communication quality.
As can be seen, a prerequisite for implementing spatial multiplexing and spatial diversity of MIMO is to employ multiple antennas to divide a space into many channels, so as to provide multiple antenna field patterns. Therefore, it is a common goal in the industry to design antennas that suit transmission demands, as well as dimension and functionality requirements.
In addition, with the advance of wireless communication technology, various wireless communication systems are developed, such as mobile communication systems (e.g. GSM, 3G, LTE), wireless local area networks (e.g. Wi-fi, Wimax), wireless personal local area networks (e.g. Bluetooth, Zigbee), etc. In order to prevent interferences among the communication systems, operating frequency bands and communication techniques, such as modulation, encoding, encryption, etc., employed by the communication systems are usually different. However, under the limitation of wireless communication resources, some of the communication systems have to share the same operating frequency band, leading to an interference issue.
For example, according to communication protocols of Bluetooth and Wi-Fi, i.e. IEEE 802.15.1 and IEEE 802.11, the operating frequency bands thereof are defined around 2.4 GHz (5 GHz employed in IEEE 802.11a) within an industrial scientific medical (ISM) band. The ISM band is world-wide reserved for industrial, scientific and medical usages, and can be utilized without permission if some regulations are followed, to prevent affecting other frequency bands. In such a situation, even though the communication protocols, modulating methods and encoding methods of Bluetooth and Wi-Fi are different, “collision” may occur because of the same operating frequency band. “Collision” herein means that a Bluetooth (or Wi-Fi) receiver simultaneously receives Bluetooth and Wi-Fi signals, leading to operating faults.
When a Bluetooth system and a Wi-Fi system collide, the Wi-Fi system can retransmit signals to a receiver based on an automatic repeat request (ARQ) scheme and decrease a transmission rate based on a rate adaptation scheme, to increase the ratio of successful transmissions. However, compared to Wi-Fi, Bluetooth is a low-power wireless connection technique. That is, a Wi-Fi signal can easily saturate a Bluetooth receiver. In detail, when a wireless receiver receives wireless signals, an amplifier gain thereof is adjusted according to transmission conditions, to efficiently convert RF signals to baseband for operations of demodulation and decoding. In such a situation, when Bluetooth and Wi-Fi collide, the Bluetooth receiver may be malfunctioned because a received Wi-Fi signal with stronger power causes the amplifier saturated. Even worse, when collision happens, a Wi-Fi transmitter decreases the transmission rate, causing a longer transmission period of a packet, such that the probability of collision is higher, finally leading to a fatal fault.
For example, a computer system accesses internet via Wi-Fi and communicates with peripherals, such as headsets, wireless keyboard, wireless mouse, etc., via Bluetooth. When collision between Wi-Fi and Bluetooth occurs, a user can still surf internet via Wi-Fi with a lower transmission rate, but cannot use the Bluetooth peripherals, which degrades utilization convenience.
Note that, Bluetooth and Wi-Fi are taken for example since Bluetooth and Wi-Fi are usually employed in the same electronic product, such as the laptop, the PDA, etc., such that collision is obvious and crucial. In general, the most effective method for improving collision is to enhance antenna isolation. However, under the limitation of spaces, increasing the difficulties of design is necessary in order to enhance antenna isolation while maintaining throughput of MIMO.
Therefore, it is a common goal in the industry to increase isolation among multiple antennas and maintain throughput under the limitation of spaces.